The movement of certain electrically-operated valves, such as certain fuel injectors, comprises a needle that is reciprocated axially within the interior of the valve's body in response to electrical energization and de-energization of an electro-mechanical actuator to thereby selectively open and close a flow path through the valve. The needle of some fuel injectors has a rounded tip end that, when the actuator is not energized, seats on a frusto-conical valve seat at the fuel injector's nozzle end to close a flow path through the fuel injector. When the actuator is energized, the needle is axially displaced to unseat its tip end from the seat and thereby open the flow path. The typical actuator is a solenoid that is mounted on the valve body and that has a guided armature to which the needle is operatively connected.
Such a fuel injector also comprises two axially spaced apart bearings that, in conjunction with the guided armature provide guidance for the axial reciprocation of the needle. For assuring proper operation and avoiding leakage when the flow path is closed, the precision and alignment of such bearing arrangements is vital. First, the bearings individually need to be highly circular. Second, they must be highly concentric, not just with each other, but also with the guided armature and the valve seat. Third, the bearings' cylindricity must be highly precise, particularly, if they have a significant length/diameter ratio. Lack of precision in the individual bearings and in their mounting arrangement on the valve body is apt to lead to loss of a fuel injector's performance. For example, faults may appear as objectionable wear, if the tolerance in the clearance of the fit between the needle and the bearings is not sufficiently strict; as objectionable leakage, if the bearings are eccentric to the valve seat, even if the bearings themselves are correctly mutually concentrically aligned; as needle jamming, if the bearings are misaligned or lack proper cylindricity; or as erratic dynamic flow, if the bearing/needle clearance is too loose and the bearings are not sufficiently precisely aligned.
Since the bearings mount on the valve body, the process of manufacturing the valve body and/or the valve body's constructional features may have an effect on the ability to secure precise bearing alignment. For instance, constructional features that are required for the valve body may impair the ability to process its manufacture in a way that is most conducive to securing a precise bearing alignment. For example, features of interest, such as bores for the bearings, are typically disposed far apart axially with the intent of providing maximum needle stability. Consequently, they are typically machined from opposite axial ends of the valve body, a process that is ordinarily completed only after multiple chuckings of the valve body. Such procedures of chucking the part, machining one end, and then re-chucking the part to machine the opposite end, inherently create some loss of accuracy. Moreover, when the outside diameter of the valve body is rough-machined by a form-tool, as it typically is for expediency, such processing may not provide sufficiently precise surfaces to which the machining of the bores for the bearings can be referenced. Thus, while it is desired that the bearing bores be spaced axially far apart for needle stability, the fact that they are machined in the manner just described undercuts the ability to attain greater precision in bearing alignment.
Accordingly, it is seen that a need exists for improving on the existing state of the art.
This need is met by providing a bearing cartridge according to the present invention. The bearings are disposed in a metal tube that is itself disposed in a bore in the valve body. The metal tube is machined to have very accurate I.D. and O.D. cylindricities and concentricity. One end of the tube is accurately counterbored to accept one bearing and a valve seat which have previously been joined together to form a bearing/seat assembly. The opposite end of the tube is also counterbored slightly larger than the outside diameter of the other bearing to allow the latter to float radially during its assembly to the tube so that it will align to the first bearing. The two bearings can thus be precisely mutually aligned, since both are installed in the tube with reference to a diameter that was accurately machined in a single chucking of the tube. The bearings and tube constitute the bearing cartridge.
The bearing cartridge can itself be accurately installed in the valve body since it has a precision O.D. and since those features of the main bore in the valve body that control the accuracy of cartridge installation can themselves be accurately machined in a single chucking of the valve body. The fact that the invention provides a fuel injector with a separate bearing cartridge opens some new processing options. The cartridge can be tested as a unit before it is assembled into the valve body, and in the unlikely event that errors are detected, the cartridge can be scrapped thereby avoiding the necessity of scrapping a completed fuel injector. Likewise, leakage testing of a cartridge/needle/actuator sub-assembly combination can be performed before final assembly into a fuel injector thereby avoiding the possibility of having to scrap completed fuel injectors if such testing is performed later and reveals that leakage is unacceptable.
The use of a cartridge also allows the valve lift to be set without the use of a lift shim, as described in commonly assigned U.S. Pat. No. 4,610,080. With the actuator fixed on the valve body, axial positioning of the cartridge will be effective to adjust the lift with all components, save the cartridge, in final position. When the correct lift is measured, the cartridge is fixed in place, such as by welding. If such welding is performed hermetically, it can seal the O.D. of the cartridge to the valve body, eliminating an otherwise required 0-ring seal.
The invention, and the features, advantages, and benefits that characterize it, are disclosed in the following detailed description of a presently preferred embodiment that illustrates the best mode contemplated at this time for carrying out the invention. The description is accompanied by drawings.